AWA: Academic Writing at Auckland

Aims and Objectives

The aim of this study is to investigate whether social learning in New Caledonian crows is essential for acquiring the ability to produce the most advanced of the tools made by the crows, the Pandanus stepped designed tool.

 More specifically, we want to determine whether juvenile crows which are never exposed to the creation or use of the stepped tools spontaneously develop the ability to do so, and whether juveniles that have undergone demonstrations of the creation and use of the tool display the behaviour either at all or at a significantly higher rate than naive juveniles.

Background and Literature review

New Caledonian crows

            New Caledonian crows, Corvus moneduloides, are renowned for their ability to manufacture and use complex tools (Kenward, Rutz, Weir & Kacelnik, 2006). In comparison with other animals that use tools, New Caledonian crows are particularly notable with reference to the frequency of tool using behaviour, the diversity and complexity of tool shapes made and used, the ability to select the most appropriate tool for a given task, and the capacity to create new tools depending on its requirement (Kenward et al., 2006). As corvids, they have the largest brain to body size ratio of all avian species (Clayton & Emery, 2005), which, as well as enabling them to use tools, also means they can form complex social groups and cache food (Emery & Clayton, 2004).

New Caledonian crow tool use and social learning

In the wild New Caledonian crows manufacture two types of tools. The first are hooked tools which are made by crafting a small hook with the beak at one end of a stick and are used to hook out insect larvae from crevices (Emery & Clayton, 2004). Pandanus tools are the second type and may be simple or stepped in design. (See Appendix, Figure 1). These consist of a strip of the edge of a Pandanus leaf so that one edge has a set of barbs. Simple tools may be wide or narrow in width and are made through a ‘cut-tear-cut’ action. Stepped tools are more complex as they require one or more additional ‘tears’ to create the steps. Though they are used in the same way as hooked stick tools they are less common. 

Unlike the use of hooked tools, which are generally thought to be genetically inherited (Kenward, Weir, Rutz & Kacelnik, 2005), Hunt & Gray (2003) propose that the stepped design arose through cultural evolution of the simple Pandanus tool and the ability to produce and use the stepped tool is maintained in a population through social transmission. 

Research questions

            To investigate whether social learning is essential for the production of stepped designed Pandanus tools in New Caledonian crows the following questions must be asked. Firstly, do naive juvenile crows develop the ability to make a stepped Pandanus tool?  And secondly, does exposing naive juveniles to the process of making stepped Pandanus tools influence their ability?

            It can be hypothesised that all juvenile crows in the study will develop the behaviour of using hooked stick tools to forage and obtain food, but only those that are allowed to observe stepped Pandanus tools being made and used will develop the behaviour.

Research design

Subjects

A total of twelve juvenile crows will be used; six females and six males. To eliminate the opportunity for juveniles to witness the process involved in making a stepped designed Pandanus tool, the juveniles are required to be born in captivity. The ten juveniles will be hand-raised together by human foster parents in artificial nests and will at no time be exposed to an adult crow (Kenward et al., 2005).

Juvenile New Caledonian crows do not tend to display specific fledging behaviours, and instead exhibit branching behaviour whereby they leave the nest to investigate their environment (Kenward et al., 2006). Thus branching, rather than fledging will be used to determine when the birds are prepared for the study to begin, as it is during this period that the crows begin manipulating objects (Kenward et al., 2006).

Hooked stick tools are considered the most simple form of tool used by the crows (Hunt & Gray, 2003, Hunt, Lambert & Gray, 2007), and are often the first of the three to be used (Weir & Kacelnik, 2006) and the most common choice in the wild (Hunt, 2000). Therefore while juveniles are beginning to display branching behaviour, they will spend a couple of hours per day in the aviary. The aviary will measure 3.5 m in length, 4 m in width, 2.5 m in height and will be on a natural daylight cycle (Kenward et al., 2006). It will contain twigs of various shapes and sizes, as well as Pandanus plants throughout the enclosure (Kenward et al., 2005). The ability to use the hooked stick tool to extract food from a hole or crevice is generally considered a ‘prerequisite’ to the use of Pandanus tools (Hunt & Gray, 2003) thus it is imperative that this skill be developed in each of the ten individuals before the study begins.

Once all of the subjects have successfully branched, and have each shown that they are competent at using twigs to extract food they will be divided into two groups, Group A and Group B, each containing three males and three females. The two groups will be housed separately.

Method

There will be two types of sessions held. To determine whether juvenile New Caledonian crows develop the ability to make stepped Pandanus tools, all birds will undergo observation sessions. Birds in Group A only will also receive one-on-one demonstration sessions.

Demonstrations will take place in the aviary. Pandanus plants will remain inside the enclosure however all twigs and sticks that could potentially be used as tools will be removed to promote the use of Pandanus as tools. One individual of Group A will be transferred from their housing arena to the aviary. Five demonstrations by the human experimenter will take place per session; one at the start then at 6 minute intervals thereafter (Kenward et al., 2006). The experimenter will tear off a strip from one of the Pandanus plants in the shape of a stepped tool design using a ‘cut-tear, cut-tear, cut-tear’ action (Kenward et al., 2005). The experimenter will then proceed to obtain a larva from a crevice using the tool by holding it upright at the wide end with the barbs facing upward. The larva will be left for the subject to eat, and the tool will be left upright in the hole (Kenward et al., 2006) so that demonstrations are similar to situations in the wild whereby the juveniles attempt to copy the behaviour of, and use tools made by their parents (Hunt, 2000). This will be repeated for all six individuals in Group A in random order.

Before each observation session commences ten larvae will be placed in crevices throughout the enclosure. The experimenter will sit in a chair inside the aviary. If the bird orients behaviour toward the experimenter it will be gently displaced (Kenward et al., 2005). Sessions will last 30 minutes or until all ten larvae have been successfully removed from the holes. Demonstration and observation sessions will take place daily until the birds have successfully made a stepped tool, or until two weeks have elapsed.

Data analysis

During the observation sessions, if an individual manipulates the Pandanus plant in any way, the bird and its general behaviour will be recorded by the experimenter. If the individual succeeded in both tearing off a strip of the Pandanus plant and using it to obtain a larva, this will be recorded. Post-use by the bird the tool will be collected and identified as a simple or stepped tool. (See Appendix, Figure 1). If no Pandanus tools were made by the individual, this will be noted.

The presence or absence of production of a simple or stepped tool will be compared between Groups A and B. If stepped tools are present in both groups, a statistical analysis will be performed to determine whether there is a statistically significant difference (p<0.05) between the number of stepped tools produced by juveniles in the two groups.

Ethics

In order for the study to take place it will first be approved by the University of Auckland Animal Ethics Committee.

Due to the social nature of corvids (Emery & Clayton, 2004, Bond, Kamil & Balda, 2002, Kenward, Rutz, Weir, Chappel & Kacelnik, 2004) individuals will never be housed alone and additionally will have frequent human social contact.

Further, corvids have a long developmental period during which they are dependent on their parents and on their peers to learn fundamental skills for survival (Clayton & Emery, 2005). As a result it is possible that separating the juveniles from their parents at birth may deprive them of certain behaviours obtained through imprinting that the human foster parents cannot offer. Typical parenting behaviours exhibited by crows will therefore be studied extensively prior to the study commencing to maximise the chances of the birds being released to the wild following completion of experiments.

Anticipated outcomes

In Kenward et al.’s (2005) study all four naive juvenile crows cut and tore up Pandanus leaves into a variety of shapes and one produced and utilised a simple Pandanus tool without any observation of an adult crow doing so, suggesting that the species has a genetically predisposed mechanism for the ability to produce Pandanus tools. However, that none produced a stepped design implies that this more advanced version is acquired through social transmission.

If social learning is essential in producing the stepped designed Pandanus tool as Hunt, Lambert & Gray (2007) and Hunt & Gray (2003) suggest, it can be expected that crows that have been given demonstrations on how to create and use the tool, Group A, will develop the capacity to exhibit this behaviour. It would also suggest that crows without tutoring, Group B, though may produce simple Pandanus tools, will not have the ability to make a stepped design. 

Practical use and Application

There is plenty of literature on New Caledonian crows’ ability to manufacture and use hooked twig tools (e.g. Hunt, 1996, Hunt, 2000, Hunt & Gray, 2004) however to date few studies have investigated the species’ abilities to make stepped designed Pandanus tools. Though the ability to make stepped Pandanus tools is presumed to be acquired through social learning (Hunt, Lambert & Gray, 2007) thus far this is simply speculation and more information is needed to better comprehend how this behaviour originates. This study will provide valuable and novel insight to the role that social learning has on the development of this behaviour and will also aid in understanding the higher cognitions of this species, in turn paving the way for future studies.

References

Bond, A.B., Kamil, A.C. & Balda, R.P. (2002) Social complexity and transitive inference in corvids. Animal Behaviour. 65:(3), 479-487.

Clayton, N.S. & Emery, N.J. (2005) Corvid Cognition. Current Biology. 15:(3), 80-81. Retrieved from Google Scholar database.

Emery, N.J. & Clayton, N.S. (2004) The mentality of crows:  Convergent evolution of intelligence in corvids and apes. Science. 306, 1903-1907

Hunt, G.R. (1996) Manufacture and use of hook-tools by New Caledonian crows. Nature. 379, 249-251

Hunt, G.R. (2000) Tool use by New Caledonian crow Corvus moneduloidesto obtain Cerambycidae from dead wood. Emu. 100, 109-114

Hunt, G.R. & Gray, R.D. (2003) Diversification and cumulative evolution in New Caledonian crow tool manufacture. Proceedings of the Royal Society. 270:(1517), 867-874

Hunt, G.R. & Gray, R.D. (2004) The crafting of hook tools by wild New Caledonian crows. Proceedings of the Royal Society. 271, 88-90

Hunt, G.R., Lambert, C. & Gray, R.D. (2007) Cognitive requirements for tool use by New Caledonian crow (Corvus moneduloides). New Zealand Journal of Zoology. 34, 1-7

Kenward, B., Rutz, C., Weir, A.A.S. & Kacelink, A. (2006) Development of tool use in New Caledonian crows: inherited action patterns and social influences. Animal Behaviour.    72, 1329-1343

Kenward, B., Weir, A.A.S., Rutz, C. & Kacelnik, A. (2005) Tool manufacture by naïve juvenile crows. Nature. 433, 121.

Kenward, B., Rutz, C., Weir, A.A.S., Chappel, J. & Kacelnik, A. (2004) Morphology and sexual dimorphism of the New Caledonian crow Corvus moneduloides, with notes on its behavior and ecology. Ibis. 146, 652-660

Weir, A.A.S. & Kacelnik, A. (2006) A New Caledonian crow (Corvus moneduoides) creatively redesigns tools by bending or unbending aluminium strips. Animal Cognition. 9, 317-334

Appendix

Figure 1: Pandanus tool designs produced by New Caledonian crows. a) and b) display a simple Pandanus tool made through a ‘cut-tear-cut’ action to produce a wide or narrow design. c) and d) display the more advanced stepped tool which require more ‘cut-tear’ steps to produce the stepped design.

(From; Hunt, G.R. & Gray, R.D. (2003) Diversification and cumulative evolution in New Caledonian crow tool manufacture. Proceedings of the Royal Society. 270:(1517), p. 868).